Bacterial-bioluminescence regulation is often associated with quorum sensing. Indeed, many studies have been made on this subject and indicate that the expression of the light-emission-involved genes is density dependent. However, most of these studies have concerned two model species, Aliivibrio fischeri and Vibrio campbellii . Very few works have been done on bioluminescence regulation for the other bacterial genera. Yet, according to the large variety of habitats of luminous marine bacteria, it would not be surprising to find different light-regulation systems. In this study, we used Photobacterium phosphoreum ANT-2200, a piezophilic bioluminescent strain isolated from Mediterranean deep-sea waters (2200-m depth). To answer the question of whether or not the bioluminescence of P. phosphoreum ANT-2200 is under quorum-sensing control, we focused on the correlation between growth and light emission through physiological, genomic and, transcriptomic approaches. Unlike A. fischeri and V. campbellii , the light of P. phosphoreum ANT-2200 immediately increases from its initial level. Interestingly, the emitted light increases at much higher rate at the low cell density than it does for higher cell-density values. The expression level of the light-emission-involved genes stays constant all along the exponential growth phase. We also showed that, even when more light is produced, when the strain is cultivated at high hydrostatic pressure, no change in the transcription level of these genes can be detected. Through different experiments and approaches, our results clearly indicate that, under the tested conditions, the genes, directly involved in the bioluminescence in P. phosphoreum ANT-2200, are not controlled at a transcriptomic level. Quite obviously, these results demonstrate that the light emission of the strain is not density dependent, which means not under quorum-sensing control. Through this study, we point out that bacterial-bioluminescence regulation should not, from now on, be always linked with the quorum-sensing control.

Although bioluminescent bacteria are the most abundant and widely distributed of all light-emitting organisms, the biological role and evolutionary history of bacterial luminescence are still shrouded in mystery. Bioluminescence has so far been observed in the genomes of three families of Gammaproteobacteria in the form of canonical lux operons that adopt the CDAB(F)E(G) gene order. LuxA and luxB encode the two subunits of bacterial luciferase responsible for light-emission. Our deep exploration of public marine environmental databases considerably expands this view by providing a catalog of new lux homolog sequences, including 401 previously unknown luciferase-related genes. It also reveals a broader diversity of the lux operon organization, which we observed in previously undescribed configurations such as CEDA, CAED and AxxCE. This expanded operon diversity provides clues for deciphering lux operon evolution and propagation within the bacterial domain. Leveraging quantitative tracking of marine bacterial genes afforded by planetary scale metagenomic sampling, our study also reveals that the novel lux genes and operons described herein are more abundant in the global ocean than the canonical CDAB(F)E(G) operon.

Abstract. Around 30 species of marine bacteria can emit light, a critical characteristic in the oceanic environment is mostly deprived of sunlight. In this article, we first review current knowledge on bioluminescent bacteria symbiosis in light organs. Then, focusing on gut-associated bacteria, we highlight that recent works, based on omics methods, confirm previous claims about the prominence of bioluminescent bacterial species in fish guts. Such host–symbiont relationships are relatively well-established and represent important knowledge in the bioluminescence field. However, the consequences of bioluminescent bacteria continuously released from light organs and through the digestive tracts to the seawater have been barely taken into account at the ecological and biogeochemical level. For too long neglected, we propose considering the role of bioluminescent bacteria and reconsidering the biological carbon pump, taking into account the bioluminescence effect (“bioluminescence shunt hypothesis”). Indeed, it has been shown that marine snow and fecal pellets are often luminous due to microbial colonization, which makes them a visual target. These luminous particles seem preferentially consumed by organisms of higher trophic levels in comparison to nonluminous ones. As a consequence, the sinking rate of consumed particles could be either increased (due to repackaging) or reduced (due to sloppy feeding or coprophagy/coprorhexy), which can imply a major impact on global biological carbon fluxes. Finally, we propose a strategy, at a worldwide scale, relying on recently developed instrumentation and methodological tools to quantify the impact of bioluminescent bacteria in the biological carbon pump.

Abstract. Around thirty species of marine bacteria can emit light, a critical characteristic in the oceanic environment where the major part is deprived of sunlight. In this article, we first review current knowledge on bioluminescent bacteria symbiosis in light organs. Then, focusing on gut-associated bacteria, we highlight that recent works, based on omics methods, confirm previous claims about the prominence of bioluminescent bacterial species in fish guts. Such host-symbiont relationships are relatively well established and represent important knowledge in the bioluminescence field. However, the consequences of bioluminescent bacteria continuously released from light organ and through the digestive tracts to the seawater have been barely taken into account at the ecological and biogeochemical level. For too long neglected, we propose to consider the role of bioluminescent bacteria, and to reconsider the biological carbon pump taking into account the bioluminescence effect (bioluminescence shunt hypothesis). Indeed, it has been shown that marine snow and fecal pellets are often luminous due to microbial colonization, which makes them a visual target. These luminous particles seem preferentially consumed by organisms of higher trophic levels in comparison to non-luminous ones. As a consequence, the sinking rate of consumed particles could be either increased (due to repackaging) or reduced (due to sloppy feeding or coprophagy/coprorhexy) which can imply a major impact on global biological carbon fluxes. Finally, we propose a strategy, at a worldwide scale, relying on recently developed instrumentation and methodological tools to quantify the impact of bioluminescent bacteria in the biological carbon pump.

Recent studies have shown the presence of an abiotic electrical current across the walls of deep-sea hydrothermal chimneys, allowing the growth of electroautotrophic microbial communities. To understand the role of the different phylogenetic groups and metabolisms involved, this study focused on an electrotrophic enrichment, with nitrate as electron acceptor. The biofilm density, the community composition, the organic products released, and the electrical consumption were monitored by FISH confocal microscopy, qPCR, Metabarcoding, MNR and potentiostat measurements. A statistic analysis by PCA showed the correlation between the different parameters in 3 distinct temporal phases. The Archaeoglobales have been shown to play a key role in the development of the community, as first colonizers and producing pyruvate, therefor used as organic source for heterotrophs. Some Thermococcales showed the ability to perform electrofermentation of this pyruvate into acetate and H2. Finally, through subcultures of the community, we showed the development of a larger biodiversity over time. This observed phenomenon could explain the biodiversity development in hydrothermal context where energy sources are transient and unstable.